1. Field of the Invention
This invention relates to the charging of fluent explosives into upwardly extending boreholes. In particular, a method and apparatus is provided whereby bulk, flowable explosives may be safely and conveniently loaded and retained in boreholes extending upwardly in the rock ceiling or roof of an underground chamber.
In the mining of underground ore bodies, boreholes for the explosive dislodgement of the ore are frequently drilled upward into the ore formation. These upwardly extending boreholes (up-holes) are charged with explosives with great difficulty, especially in chambers having high ceilings. One or more explosive charges in packages are fitted into the mouth of the borehole and, thereafter, lifted and pushed manually by means of a loading pole into the borehole where they must be secured against the force of gravity. Packaged explosive charges, for purposes of economies in many mining operations, have been superceded by explosives in unpackaged or bulk form. These bulk explosives, such as, for example, pulverulent ANFO, water-gel slurries and water-in-oil emulsions, are provided near the blasting site in bulk containers from which they are delivered directly into the boreholes by air-eduction or pumping methods. The loading of these flowable bulk explosives into up-holes has presented particular difficulties for mine operators.
2. Description of the Prior Art
Attempts to charge up-holes with flowable explosives have generally involved the use of an explosive delivery pipe or hose fitted tightly into the borehole and equipped with a valve or other device which prevents flow-back of the fluent explosives from the charged hole. Often special seals are required to provide fluid-tight closure of the boreholes. U.S. Pat. No. 4,036,100 granted June 19, 1977 to E. K. Hurley attempts to provide a simplified and practical means for charging up-holes. However, the method of Hurley has not, to Applicant's knowledge, been adopted commercially. One problem not overcome by the Hurley method is the entrapment of air within the borehole during the loading of the fluent charge. A further solution is offered in U.K. Patent Specification No. 1,393,859 by a method wherein the vicinity of the collar of the borehole is stoppered and a pumpable explosive is introduced into the borehole to occupy the volume of the borehole progressively from the collar to the toe of the hole. In this method, an increasing volume and weight of explosive must be overcome by the pump in order to fill the borehole. Furthermore, a closely-fitted stopper or plug is required to prevent loss of explosives from the borehole.